NEODYMIUM ISOTOPIC CONSTRAINTS FOR THE ORIGIN OF MESOPROTEROZOIC FELSIC MAGMATISM, GAWLER-CRATON, SOUTH AUSTRALIA

Mesoproterozoic felsic magmatism of the Gawler Range Volcanics and Hiltaba Suite granites occurred at 1585-1595 Ma across much of the Gawler Craton, South Australia. Nd isotopic analysis of this felsic magmatism, combined with petrological and geochemical arguments, suggest derivation by partial melting of both Paleoproterozoic and Archean crust. The majority of samples analyzed have Nd isotopic and geochemical characteristics compatible with the involvement of Paleoproterozoic crust stabilized during the 1.85-1.71 Ga Kimban orogeny as sources for the Mesoproterozoic magmatism; others require derivation from sources dominated by Archean rocks. This cycle of Paleoproterozoic crustal stabilization followed by involvement of this crust Mesoproterozoic felsic magmatism is one previously documented from many parts of Mesoproterozoic Laurentia. On the basis of models proposing East Australia - Antarctica to be the conjugate landmass at the rifted margin of western North America, it appears that the voluminous magmatism of South Australia is another example of a typically Mesoproterozoic style of magmatism linked to Laurentia. This Mesoproterozoic magmatism appears temporally Linked to regional high-temperature, low-pressure metamorphism of the region, and together with the presence of mantle-derived magmas, implicates the operation of large-scale tectonothermal processes in the origin of felsic magmatism at 1590 Ma.